The present invention relates to systems for delivering a stent from a sheath positioned at the distal end of a delivery catheter. Specifically, the invention relates to systems configured to draw back a sheath surrounding a stent, while simultaneously pushing the stent distally from the interior of the sheath.
It is well known in the prior art to deliver self expanding stents from the distal end of a delivery catheter. Typically, a self-expanding stent is compressed into a first condition and inserted into a distal sheath that holds the stent in the first condition at the distal tip of the catheter. A stent engagement member, comprising an angled barb, may reside within an inner lumen of the stent prior to activation. Upon activation of the delivery system, and in a series of small repetitive actions, the sheath may be withdrawn, and subsequently the stent engagement member may push distally to engage with the stent and force the stent distally further outside of the sheath. It is typical that up to ten or twenty small movements involving sheath withdrawal and stent advancement may be undertaken before the stent is entirely deployed out of the sheath.
Problems arise in the prior art however. One problem is that the mechanical actions of withdrawing the sheath and pushing the stent do not typically take place simultaneously, but take place sequentially. This gives rise to a situation in which the sheath tends to frictionally drag the stent proximally when the sheath is withdrawn during an incremental movement, thereby displacing the stent on the catheter axis, and also compressing (i.e. shortening) the stent along its axis. Such compression may further result in the stent expanding radially by a small amount. This effect is problematic because the next incremental action, which is to push the stent distally, is complicated by the fact that the stent may have changed its location on the catheter and also may have changed its shape. In extreme situations, the mechanism designed to move the stent distally may be inoperable, because contact between the engagement member and the stent may have become disengaged. Another problem that arises in the prior art is that push and pull mechanisms designed to deploy self expanding stents from a sheath typically are not operably linked with each other. This has the result that a certain movement by the sheath does not correspond with a fixed amount of movement by the stent. Rather, the amount of movement of the push (stent) and pull (sheath) mechanisms are independent of each other and are determined by the physician user, who is often obliged to guess how much movement she has achieved with each mechanism after a certain amount of time, and how much further movement is needed.
Thus there is a need in the art for a delivery system that addresses the problems in the art. The present invention addresses these and other needs.